The experienced grower harvests his crop when 50 to 80% of the pistles have turned color.
You can't just go off of hairs. One of my White Chocolates has
5 white pistils left, but the trichs aren't matured yet. THCA bio-synthesis needs to be looked at first, followed by the pistil withering and calyx swelling
Also, have you ever let one go a little longer and seen how it is? I've gotten impatient and cut a few girls down when the hairs were exactly when you say to cut, the high was weak. If the pot you grow is the best you've ever had, then you wouldn't realize it hasn't reached its potential.